Improved double connected inverter for reducing output voltage harmonics

The authors propose a new method for reducing harmonic components involved in the output voltages of the double connected inverter. By adding four auxiliary switching devices and an interphase transformer with a secondary winding into the input DC side of the usual 12-step inverter, the proposed circuit can decrease the output voltage harmonics no less than the conventional 36-step inverter. Basic theories are discussed by analyzing the output voltage waveforms, and optimum parameters are derived, and the effects of harmonic reductions are recognised by both theoretical and experimental results. Moreover, the authors try to suppress surge voltages impressed to switching devices by stray inductances on the equipment wirings in the input DC side. By applying auxiliary suppressive circuits similar to the usual snubber circuit, the authors confirm by experiments that they can be restrained